When a cathode follower shares the same triode and load resistance and plate voltage and idle current as the grounded-cathode amplifier that precedes it, the cathode follower undoes much of the distortion of the first stage. This happens because the cathode follower is retracing the curves that the grounded-cathode amplifier traced. As the first stage's plate sluggishly swings positive, its cathode-to-plate voltage increases and its conduction decreases; as the cathode follower's cathode swings positive, its cathode-to-plate voltage aggressively decreases and its conduction increases. Inversely, when first stage's plate aggressively swings negative, the cathode follower's cathode-to-plate voltage sluggishly increases and its conduction decreases.
      To the degree that a triode is consistently inconsistent, this circuit will make use of inverse pre-distortion to yield a lower distortion than either sub-circuit used independently. If this technique seems too optimistic, consider what goes on a multiple stage line amplifier with feedback; the penultimate gain stage delivers to the last stage an inverse pre-distorted signal that undoes the distortion that the last would impose in the absence of feedback. The feedback created this inverse pre-distorted signal precisely for the output device, as it is the output device that terminates the feedback loop. (It is interesting to compare a non-feedback amplifier to one with feedback. In the non-feedback amplifier, distortion grows larger at each proceeding stage from the input. In the feedback amplifier, distortion is largest at the input stage and grows cleaner with each proceeding stage to the output.) But feedback is not the only means to creating an inverse pre-distorting signal.
      How do we use this trick to make a power amplifier? First of all, we must use the same triode type for both the driver tube and the output tube. Second, we must use same cathode-to-plate voltages, load impedances, and idle currents for both triodes. Third, we must cascade a grounded-cathode amplifier into a cathode follower output stage.

      At first glance, it looks like we will have to lose half of the potential power output in order to reduce the distortion complementarily, as the first stage will have to work into the same load as will the output stage. For example, if the a single 2A3 output tube sees a load of 2500 ohms, then the 2A3 driver tube will also have to work into a 2500 ohm load; since both tubes undergo the same voltage and current swing, both tubes will deliver the same power into their loads. But as only one of these loads creates sound, half of the potential efficiency is lost. Considering that the average triode based SE amplifier is only about 20% efficient, we do not have much efficiency to throw away.
      But if we increase the number of output devices used in parallel, we effectively increase the efficiency. For example, if we design a single-ended 300B power amplifier that uses three 300B output tubes in parallel, then only one 300B power tube is needed to provide the complementary inverse pre-distortion. So we end up throwing away only a quarter of our potential watts, rather than half. (Of course, the more output tubes in parallel, the better the efficiency.)   

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